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HELP Example Question (Conic Projection Lesson Pg23)

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  • HELP Example Question (Conic Projection Lesson Pg23)

    Hi, struggling to grasp how the chart convergency is calculated to be 4 degrees from the Lambert's Calculation question at the end of the conic projections lesson (I have attempted to put a screenshot below, but not overly confident the format will work).

    I cannot see how the convergency equation is being utilised- help needed!

    Thx!
    Attached Files

  • #2
    The difference between the great circle track and the rhumb line track at the start of the journey at Rakovnik is 2 degrees (270 rhumb line track along a parallel of latitude and the given initial true track of 272). This difference is the Conversion Angle. The Conversion Angle is half the convergency so we know that the convergency is 4 degrees.

    CONVERGENCY = CHANGE OF LONGITUDE X SINE OF PARALLEL OF ORIGIN

    The sine of the parallel of origin on a Lambert's chart is known as the Convergence Factor, the Constant of the Cone or simply 'n'.

    So

    4 degrees = 5 degrees 3.2 minutes x constant of the cone

    So 4 degrees / 5 degrees 3.2 minutes = constant of the cone

    So constant of the cone = .792

    Answer a is correct

    Hope this helps

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    • #3
      Thanks very much, that all makes sense now.

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